Repair is most likely to replace the crankset - I don't know how the halves are attached to the arms.

The likely cause is that the hirst joint bolt was loose - judging by the fretting of the joint. One imagines that once its loose and allowed to fret it is probably a risk of breaking the bolt, as that will transfer load from the joint to the bolt. (the broken thing in the picture is the bolt).

I think its a rare failure, put down to no-one ever checking it properly.

Last edited by zero on Mon Oct 01, 2012 8:12 pm, edited 2 times in total.

From the images provided it appears the internal Ultra Torque bolt that holds the two crank sides together has been sheared. It may have been over torqued and fatigued. If you can extract the sheared bolt section out of the two crank halves and the threads are intact then you simply replace the bolt as the splines look perfect (at least the ones I can see in the pics)

zero wrote:Repair is most likely to replace the crankset - I don't know how the halves are attached to the arms.

The likely cause is that the hirst joint bolt was loose - judging by the fretting of the joint. One imagines that once its loose and allowed to fret it is probably a risk of breaking the bolt, as that will transfer load from the joint to the bolt. (the broken thing in the picture is the bolt).

I think its a rare failure, put down to no-one ever checking it properly.

Hi Zero,

Thanks for your feedback. The bike was taken to the bike shop for a total overhaul when I got it. Would it be a possibility that it was an oversight by the mechanic?

open roader wrote:From the images provided it appears the internal Ultra Torque bolt that holds the two crank sides together has been sheared. It may have been over torqued and fatigued. If you can extract the sheared bolt section out of the two crank halves and the threads are intact then you simply replace the bolt as the splines look perfect (at least the ones I can see in the pics)

Hi Open Roader,

That is something I will need to check with the shop tomorrow. I can't see how the metal can fatigue when the total km of the groupset has done roughly 7000km with a major overhaul in April this year. :S

My bet is that you can fix this for the cost of a new Ultra Torque bolt. If the bike shop says they want to sell you a new crank set then go elsewhere as I'm 99% sure I could fix this one myself.

It's easy to overtorque a bolt like this and re-checking the torque level is perhaps not on the highest priority of a shop mechanic when he/she is performing a once over for a 2nd hand purchase. purchase.

open roader wrote:From the images provided it appears the internal Ultra Torque bolt that holds the two crank sides together has been sheared. It may have been over torqued and fatigued. If you can extract the sheared bolt section out of the two crank halves and the threads are intact then you simply replace the bolt as the splines look perfect (at least the ones I can see in the pics)

Hi Open Roader,

That is something I will need to check with the shop tomorrow. I can't see how the metal can fatigue when the total km of the groupset has done roughly 7000km with a major overhaul in April this year. :S

If you stress steel below 50% of yield, it will usually do many millions of cycles between failures. if you stress it well past 50% of yield, then it can fail in thousands of cycles.

having read around, there is a clip that can be had to stop the whole thing falling out if it fails, and overtorque failures are supposed to be uncommon but fairly common amongst the hamfisted owners without torque wrenches.

I'll go with open roaders answer and hopefully it should be cheap. That half of the bolt looks easily removed as it still has its square surfaces.

open roader wrote:My bet is that you can fix this for the cost of a new Ultra Torque bolt. If the bike shop says they want to sell you a new crank set then go elsewhere as I'm 99% sure I could fix this one myself.

It's easy to overtorque a bolt like this and re-checking the torque level is perhaps not on the highest priority of a shop mechanic when he/she is performing a once over for a 2nd hand purchase. purchase.

Hi Open Roader,

Thanks for your advice! Like you said, the shop was going to get me a new crank but when I was about to walk out they mentioned that they could fix it.

But they have no idea how much it would cost as they don't have the part and will need to order it in.

I would have thought that they will pay a lot more attention considering I ask for a full service which they charged me a pretty penny.

open roader wrote:From the images provided it appears the internal Ultra Torque bolt that holds the two crank sides together has been sheared. It may have been over torqued and fatigued. If you can extract the sheared bolt section out of the two crank halves and the threads are intact then you simply replace the bolt as the splines look perfect (at least the ones I can see in the pics)

Hi Open Roader,

S

If you stress steel below 50% of yield, it will usually do many millions of cycles between failures. if you stress it well past 50% of yield, then it can fail in thousands of cycles.

having read around, there is a clip that can be had to stop the whole thing falling out if it fails, and overtorque failures are supposed to be uncommon but fairly common amongst the hamfisted owners without torque wrenches.

I'll go with open roaders answer and hopefully it should be cheap. That half of the bolt looks easily removed as it still has its square surfaces.

Hi Zero,

I don't work on my bike with the exception of general clean and maintenance as I don't have a torque wrench and knowing how easy to crack a road bike.

That's the reason I visit that shop on a regular basis for servicing and assembly.

Ham fisted owners sans torque wrenches or otherwise, this is a rare occurance in my books. If you can re-fit a new ultra torque bolt and you are guaranteed it's torqued to 40Nm then it's very unlikely to ever be an issue again.

open roader wrote:Ham fisted owners sans torque wrenches or otherwise, this is a rare occurance in my books. If you can re-fit a new ultra torque bolt and you are guaranteed it's torqued to 40Nm then it's very unlikely to ever be an issue again.

Hi Open Roader,

Went to the shop and they have confirmed that it must have been over tighten as the groupset has done no more than 7000km. Too early for the ultra torque bolt to fail.

They will re-check everything for me to make sure all bolts are torque to the right spec. Can't have bits and piece flying off during a decent down a hill.